Yazar "Alli, Abdulkadir" seçeneğine göre listele

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    Dielectric properties of CdSe quantum dots-loaded cryogel for potential future electronic applications
    (Elsevier Sci Ltd, 2020) Cadirci, Musa; Sarkaya, Koray; Alli, Abdulkadir
    Cryogels are an outstanding class of materials with special and functionalized physical properties in various fields and privileges for different industrial applications. Due to unique properties of quantum dots, properties of cryogels can be engineered by adding quantum dots in. In this study, both p(HEMA)-based cryogel and CdSe QDs synthesized and characterized, separately. Then, CdSe QDs were loaded into p(HEMA) cryogels by immersing cryogel into QDs solutions. FTIR-ATR, SEM and TGA characterizations were performed to ensure that CdSe QDs penetrate p(HEMA) cryogels effectively. Dielectric properties of CdSe QDs-loaded cryogel were investigated using Electrical Impedance Spectroscopy (EIS). Real and imaginary parts of dielectric constants were decreased significantly at low frequencies in QD-loaded cryogels. While real part of impedance was increased in CdSe QDs-loaded cryogel at low frequencies. In addition, at high frequencies, those parameters were observed to be same in both cases.
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    Investigation of the Performance of Poly(Methyl-Acrylate) as a Gate Dielectric in Organic Thin-Film Transistors
    (Springer, 2020) Yardim, Tayfun; Demir, Ahmet; Alli, Sema; Alli, Abdulkadir; Yucedag, Ibrahim
    In this study, we present two regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT)-based top-gate bottom-contact configured organic thin-film transistors (OTFTs) using poly(alpha-methyl acrylate) (PMA) and poly(methyl methacrylate) (PMMA) polymers separately as gate insulators for comparison. In order to compare only the performance of the dielectrics, the other parts of the devices were kept qualitatively and quantitatively identical. Unlike PMMA, PMA is flexible, and flexibility is a desirable property for an OTFT. Thus, utilizing PMA can be advantageous if it supports higher performance of the transistor. In this respect, the electronic parameters of the fabricated devices were extracted from transfer and output characteristics to determine the performance of PMA in OTFT applications. Results showed that the mobility of the OTFT with PMA (PMA-OTFT) was nearly three times greater than that of the OTFT with PMMA (PMMA-OTFT), while the PMA-OTFT threshold voltage (V-TH) was slightly less than that of the PMMA-OTFT, which was likely because of the greater effective capacitance (C-EFF) of the PMA layer compared to that of the PMMA layer. This is the main advantage of the PMA. On the other hand, the major downside is found in the reduced on-to-off current (I-ON/I-OFF) and increased subthreshold swing originating from a huge off-current (I-OFF), implying the existence of a large gate leakage current. Increasing the thickness of the PMA layer could reduce such large gate leakage current. However, this would lead to additional increase in the OTFT operating voltage. Therefore, further studies are required to improve the insulating property of the PMA polymer in order to substitute it for the PMMA.
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    One-step preparation of poly(NIPAM-pyrrole) electroconductive composite hydrogel and its dielectric properties
    (Wiley, 2021) Sarkaya, Koray; Yildirim, Mert; Alli, Abdulkadir
    Conductive polymers and hydrogels are two of the hot prospect polymer types that are used for new stimuli responsive materials. In this study, one-step preparation of electroconductive composite hydrogels containing polypyrrole (PPy) and N-isopropylacrylamide (NIPAM) using free radical polymerization technique was achieved with N,N-methylenebisacrylamide as a crosslinker and ammonium peroxy disulphate (APS) as initiator, in mixture of water/isopropyl alcohol. The equilibrium swelling degree of the poly(NIPAM)-pyrrole) electroconductive composite hydrogel was 9.88 g of H2O/g dry polymer. According to TGA results, the thermal stability of the prepared composite poly(NIPAM-PPy) conductive hydrogel (700 degrees C) hydrogel is higher than that of pure poly(NIPAM) hydrogel (600 degrees C). Furthermore, prepared samples were characterized by FTIR, and SEM analyzes. Later, the samples were pressured into pellets so that electrical impedance spectroscopy (EIS) measurements were taken between 10 and 10 MHz at room temperature. The dielectric constant value of composite poly(NIPAM-PPy) hydrogel at 10 Hz is almost 10 times higher than that of poly(NIPAM) hydrogel. Both samples' real and imaginary parts of dielectric constant decreased with increased frequency. Samples exhibited non-Debye relaxation since experimental data fit into dielectric model of Havriliak-Negami. Moreover, low frequency data yielded d.c. conductivity of the pure and composite samples as 3.74 x 10(-11) and 1.02 x 10(-8) S/cm, respectively. Real part of impedance at low frequencies also points out similar to 10(3) times lower resistance values at 10 Hz for composite poly(NIPAM-PPy) hydrogel. Therefore, EIS results support that electroconductive composite hydrogel fabrication was achieved using free radical polymerization technique.
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    Synthesis and characterization of cryogels of p(HEMA-N-vinylformamide) and p(HEMA-N-Vinylpyrrolidone) for chemical release behaviour
    (Springer, 2021) Sarkaya, Koray; Alli, Abdulkadir
    Macroporous polymeric gels has received great attention in many fields focused on biotechnological applications. In this study, two new HEMA-based cryogel columns were synthesized. To this end, poly(HEMA-VF) and poly(HEMA-NVP) cryogels were prepared by copolymerization of 2-Hydroxyethyl methacrylate (HEMA) with N-vinylformamide (VF) and N-vinylpyrrolidone (VP) in the presence of N,N-methylenebisacrylamide (as cross-linker), then polymerization initiated by ammonium persulfate (APS) and N,N,N ',N '-tetramethylenediamine (TEMED) with free-radical polymerizations method in cryogelation conditions, respectively. p(HEMA-VF) and p(HEMA-VP) cryogels contain a continuous polymeric matrix with interconnected pores of size 2-100 mu m. Swelling behavior for these cryogels in various solvents was investigated, wherein the characterization of the cryogels is conducted via by surface area measurement (BET), Fourier transforms infrared spectroscopy (FT-IR), elemental analysis, scanning electron microscopy (SEM), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). As drug model compounds, Methyl Red (MR), methylene blue (MB) and methylene green (MG) were loaded into prepared cryogels and the controlled release properties of cryogel columns were examined comparatively each other. It has been shown that approximately 90% of its release from the cryogels occurred within about 2 h. In addition, MB release from p(HEMA-VF) and p(HEMA-VP) cryogels was found to be around 80% over a similar period. The proposed cryogels can be regarded as controlled release system on future biomedical applications.
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    Synthesis and electrical characterization of poly[(linoleic acid)-g-(styrene)-g-(?-caprolactone)] graft copolymers as gate insulator for OFET devices
    (Wiley, 2023) Gurel, Murat; Cavus, Fatma Kosovali; Demir, Ahmet; Doganci, Erdinc; Alli, Abdulkadir; Alli, Sema
    This study reports a one-pot process used to synthesize poly[(linoleic acid)-g-(styrene)-g-(epsilon-caprolactone)] (PLina-g-PSt-g-PCL) graft copolymers. The process was carried out by combining the atom transfer radical polymerization of styrene with the ring-opening polymerization of e-caprolactone from polymeric linoleic acid having hydroxyl groups and bromine groups in the main chain. The characterization of the products was achieved using proton nuclear magnetic resonance, size-exclusion chromatography, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry techniques. Subsequently, an organic field effect transistor (OFET) was fabricated with PLina-g-PSt-g-PCL graft copolymers as the insulator layer. Poly(3-hexylthiophene) (P3HT) was used as the active layer and prepatterned OFET substrates were used as the welding/discharge electrodes. To measure capacitance, an ITO/P3HT/PLina-g-PSt-g-PCL/Al structure was prepared using the same method. To obtain output and transfer current-voltage characteristics, electrical characterizations of OFET devices were conducted in darkness and an atmosphere of air. From a capacitance-frequency plot, the key characteristics of the devices, including the threshold voltage (V-Th), field effect mobility, and current on/off ratio (I-on/off), were derived. The fundamental electrical parameters in the fabricated OFET devices based on styrene concentration were thoroughly examined. It was observed that the produced PLina-g-PSt-g-PCL OFETs display positive device characteristics such as low V-Th, exceptional mobility, and I-on/off values. (c) 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.
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    ULTRAVIOLET ILLUMINATION RESPONSIVITY OF THE Au/n-Si DIODES WITH AND WITHOUT POLY (LINOLENIC ACID)-G-POLY (CAPROLACTONE)-G-POLY (T-BUTYL ACRYLATE) INTERFACIAL LAYER
    (World Scientific Publ Co Pte Ltd, 2020) Gursel, Umit; Taran, Songul; Gokcen, Muharrem; Ari, Yurdagul; Alli, Abdulkadir
    Au/n-Si (MS) and Au/Poly (linolenic acid)-g-poly (caprolactone)-g-poly (t-butyl acrylate) (PLilPCLPtBA)/n-Si (MPS) diodes were fabricated to investigate the electrical and responsivity effects of interfacial layer on the diodes under ultra violet (UV) illumination. Electrospinning method was used for coating of the PLilPCLPtBA polymer layer on n-Si single crystal as nanofibers. Surface formation and nanofiber characteristics of the polymer layer were investigated by an electron microscope. The current-voltage (I-V) measurements of the MS and MPS diodes were carried out in dark and under UV (365 nm) illumination conditions at room temperature. Basic electrical parameters of the diodes; such as reverse bias saturation current (I-0), zero bias barrier height (Phi(B0)), ideality factor (n), series resistance (R-s) and interface state density (N-ss) were extracted from the experimental I-V measurements by thermionic emission and Norde equations. Also, power law of the photocurrents (I-pc) and responsivity (R) behavior were obtained and given comparatively.